Commutator brush unit



Feb. 8, 1966 J. LINDNER 3,234,420

COMMUTATOR BRUSH UNIT Filed Feb. 1, 1961 2 Sheets-Sheet 1 P( i :1 F/G.7 2 i' I f/ VENTOR:

Josef L in dn Gr 53 minim-J 3'- ..ATTO (LN E :55

Feb. 8, 1966 J. LINDNER 3,234,420

COMMUTATOR BRUSH UNIT Filed Feb. 1, 1961 2 Sheets-Sheet 2 C! FIG. 10

F7677 F76. 72 FIG.

, I/VVENTUR: Josef Linc/ne ozLekoroLsT g A ORNEQS United States Patent M 3,234,420 COMMUTATGR BRUSH UNIT Josef Lindner, 8 Theresienplatz, Nurnberg, Germany Filed Feb. 1, 1961, Ser. No. 86,514 Claims priority, application Germany, Feb. 4, 1960, W 27,183; July 26, 1960, W 28,242 2 Claims. (Cl. 310-244) The present invention relates to improvements in cornmutator brushes, especially for miniature motors, and more particularly to a brush of the type consisting of a leaf spring and a gauze of thin, highly conductive wire which is secured to this spring.

Such commutator brushes have to comply generally with the following requirements. The contact resistance and the friction between the brushes and the commutator must be very small in order to insure that the brushes will last for a long time. Furthermore, the. brushes should produce very little noise. Most of the commutator brushes of this type which are already known comply with these requirements to some extent. In these known brushes, the wire gauze is soldered along its entire surface to the leaf spring. Although the contact resistance and the coefficient of friction of these known brushes is relatively small, it is always found when they are used in a continuous operation, especially if the brushes do not fully engagewith the commutator, that the current load on individual points of the wire gauze is very high so that the losses due to abrasion and burning-off are also very high.

It is an object of the present invention to provide a commutator brush unit of the above-mentioned type which overcomes these disadvantages and produces a very small contact resistance and friction and insures that the current load on the wire gauze will be as uniform and small as possible so that the losses due to abrasion and burning-off will be reduced to a minimum.

According to the present invention, this object will be attained by providing the wire. gauze in the form of a bandlike strip and by providing the leaf springs at both sides of the commutator with projecting edges on which the bandlike gauze is supported when it is pressed by the respective leaf spring against the commutator. ,Since the wire gauze possesses a certain amount of elasticity, it will to some extent also yield elastically under the pressure which is exerted by the leaf springs, and it will therefore engage with the commutator under a certain initial tension and at a relatively large looping angle. Due to this large looping angle and the resulting large contact surface, the specific current load will be very small so that, at a proper contact between the wire gauze and the commutator, the contact resistance and friction will be very small and the arcing as well as the losses due to abrasion and burning-off will be reduced to a minimum.

In order to provide the leaf springs with the projecting edge portions for supporting the bandlike wire gauze, each leaf spring is bent at its end .portion adjacent to the commutator so as to have a shallow U-sha-pe so that the ends of the side arms of this U-shaped portion will form the supporting edges. The bandlike gauze strip which may consist of one or several layers only needs to be secured to the leaf spring at a point spaced from the U-shaped end portion, and it may be either soldered or riveted thereto.

It has, however, been found to be of advantage if the wire gauze is also secured, and preferably soldered, to

3,234,420 Patented Feb. 8, 1966 the outer edge of each leaf spring. When applying this embodiment of the invention, the elasticity of the leaf spring will also be utilized so that the wire gauze itself may be of a lower elasticity. In order to make the commutator-end of the leaf spring slightly more softly elastic, it is preferably slotted between the mentioned contact edges thereof. It will then yield more easily when the gauze is pressed against the commutator.

According to another feature of the invention, the installation of the commutator brushes will be greatly facilitated by securing the leaf springs at their ends where they are free of wire gauze to a supporting plate or bracket of plastic. The springs may, for example, be secured in the supporting bracket by injection molding, although they may, of course, also be clamped within the supporting bracket. For attaining a very simple electrical connection of each leaf spring it is provided with a rectangular projection which serves as a soldering terminal and is bent over for securing the leaf spring which is clamped into the supporting bracket. 'Ihis bracket may also be provided with a pair of lateral bores for mounting it in a fixed position.

Another feature of the invention consists in making the bandlike wire-gauze strip in the form of a flat roll which consists of several layers or windings and the central axis of which rests on the leaf spring in the longitudinal direction thereof, while one of its ends is secured to the leaf spring. A further feature of the invention resides in simplifying the manufacture and assembly of the commutator brush unit by soldering or welding the roll of wire gauze to each leaf spring at the end of the roll which faces toward the free end of the leaf spring.

Although it has already previously been proposed to utilize bandlike wire-gauze strips for making commutator brushes by folding the gauze around the freely movable end of the leaf spring and by then soldering it at both sides to the leaf spring, such gauze consisted of only a few layers and was therefore soon worn through in operation. Such a structure also had the serious disadvantage that, after the wire gauze was worn through, the commutator came into contact with the leaf spring so that the contact resistance then increased very strongly and the leaf spring was eventually even destroyed. Furthermore, after the bandlike wire gauze was worn through, the frayed ends thereof projected and interfered with the operation of the motor.

Contrary to these prior commutator brushes, the brushes according to the invention are made of bandlike wire-gauze stripes which are wound into rolls which are flattened either by being wound in a flat condition or by being pressed flat after being wound in order to attain the largest possible contact surface relative to the commutator. in-ce such a fiat roll consists of a large number of windings or layers, the gauze strip has the advantage of being very elastic. Furthermore, the commutator brushes according to the invention have a very long life due to the fact that the motor may run for a very long time until all of the layers of wire gauze will be worn through. The fine metal dust which is formed by the abrasion of the wire gauze becomes firmly deposited in the pores of the gauze and thereby increases the surface area of the brushes which, in turn, results in a reduction of the contact resistance on the commutator. The fine metal dust is therefore absorbed by the gauze and will therefore not be deposited at any other places, such as on the hearings or on points of insulation where it mightform conductive bridges and cause insulation failures. On the other hand, the abrasion of the wire gauze results in a reduction of the contact pressure caused by the leaf springs, since the springs will then move more closely to the commutator whereby their tension will be decreased. This reduction of the contact pressure would normally result in an increase in the contact resistance. However, the mentioned increase of the surfacearea, of the Wire gauze and the reduction of the tension of' the leaf springs compensate each other tosuch-an extentthat the contact resistance will remain practically unchangedat all times. This constitutes a very important advantage of the commutator brushes according to the'invention.

These objects, 'features,iand advantages of the present invention wil-lx'become stillmore clearly apparent from the following detailed description which is to be read with reference fto fthe accompanying drawings, in which FIGURE 1 shows'aside view of a commutator brush unit .according to the invention;

FIGURE 2 shows thebrushesaccording to FIGURE 1 in engagement withna commutator;

FIGURE 3 shows a cross section taken along line IIIIII of. FIGURE 2;

FIGURE4 shows aside view of a modification'of the commutator-brush unit according to the invention;

FIGURE 5 shows the brushes according to FIGURE'4 in engagement with a commutator;

:FIGURE 6 shows a cross section taken along line VI-VI of FIGURE 5;

FIGURE 7 shows a top view of the supporting bracket with commutator'brushes according to FIGURES 1, 2, 4, and 5 inserted therein;

FIGURE 8 shows a band of gauze of-fine copper wire;

FIGURE 9-shows the band of wire gauze according to'. FIGURE 8 after it is wound to form a roll;

FIGURElOshows a cross section taken along line X- X of FIGURE 9;

FIGURE 11 shows a side view of another modification of the commutator brush unit according to the invention;

FIGURE 12shows the brushes according to FIGURE 11in engagementwith a commutator;

FIGURE 13shows a cross-section taken along line XI-II'XIII of FIGURE 12; while FIGURE 14shows. a top view of the commutator brush unit. according to FIGURE 11.

The commutator brush unit according to the invention as illustrated in FIGURES Ito 7 consists of a pair of leafsprings Land-2 and of strips 5 and 6 of wire gauze which are'soldered toleaf springs 1 and 2 at 3 and 4. As indicated in these drawings, gauze strips'5-and'6 consistof two superimposed layers. The lower end portionsiof leafsprings"1 and 2 are substantially U-shaped so that on each spring a pair of edges"7,8 or-9, 10, respectively, is formed. These edges engage with and support the gauze strips 5 and 6 when the latter are pressed against the commutator 11, as indicated in FIGURES 2, 3, 5, and 6 in dot-and-dash lines. Gauze strips 5 and 6 thereforedo not-engage withleaf springs 1 and 2 within the area inter-mediate the edges'7 and 8 or 9 and of the springs. Edges 8 and 10 may also be rounded off or they maybe bent so as to be rounded. In order to make the U-shaped ends ofleaf springs =1 .and 2 more softly elastic,- they may be provided with slots 12 and 13 intermediate the edges'7, 8 and 9, 10, respectively.

In the embodiment of the-invention according to FIG- URES 4 and 6, the gauze strips 5 and 6 are soldered to the edges-8 and 10 of leaf springs 1 and 2 so that, when these gauze strips are pressed against the commutator 11, the U-shaped ends of leaf springs 1 and 2 will be bent in the longitudinal direction, as shown'particularly in FIGURE 5. 'This embodiment has the advantage'that, When'the commutator brushes are inserted into the motor,

4', the ends of the gauze strips will not be accidently. bent, and further that the relatively high elasticity of springs 1 and 2 will insure that the tension of gauze strips 5 and 6 will always remain uniform.

At the upper ends of leaf springs 1 and 2 which are free of the gauze strips, the springs are inserted and secured in oblique slots 14 and 15 in a supporting bracket 16 which consists of plastic. Slots 14 .and 15 are made of a sufiicient width so as also to accommodate clamping strips 17 therein by means of which leaf springs 1 and 2 may be clamped securely to bracket 16. These clamping strips 17 are illustrated particularly in FIG- URES 3 and 6. For the electrical connections, leaf springs 1 and'2 are provided with rectangular extensions 18 which project through the slots 19' in supporting bracket 16. Clamping strips 17 are also provided with extensions 2t which likewise engage into slots 19 of bracket 16 for clamping the extensions 18 of the leaf's prings. For securing leaf springs 1 and 2 in a fixed=position"in bracket 16, extensions 18 maybe bent at 'an angle; as illustrated particularly in FIGURE 7. These extensions 18 may also be used as soldering terminals. Bracket 16 is further provided with'a pair of bores 21 and 22for mounting it on the motor. I v v V The commutator brushes, as shown inFIGURES 1 to 7, which are secured in bracket 16 form a structural'unit which may be easily inserted and'secured' in a'directcurrent motor.

FIGURE 8 illustrates a strip 23 which c'onsistsof afine gauze of thin copper wire. This strip 23'is then'wound up to form a fiat roll 24, as shown in FIGURES 9 and 10 which consists of several windings. A pair of such rolls 24 is placed upon leaf springs25 and 26,-as shown in FIGURES 11 to 13 and they are then either welded or soldered to the lower ends of the springs at 27 and-28. The upper ends'29 and 30 of leaf springs25 and'26 are bent over, and these bent portions are secured to a solid strip of insulating material, such as hard paper or the like. At 29' and 30, a pair of conductors 32 and 33 may be soldered to the bent-over ends of springs 25 and 26. When leaf springs 25 and 26 with the gauze rolls 24thereon are applied upon the commutator 34, the springs will be spread apart, as illustrated in FIGURE 12, and will thereby be given the required tension to press the gauze rolls 24 with the desired contact pressure'against'the commutator 34.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capableof numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, What I claim is:

1. A commutator brush unit fora miniature motor, comprising a pair of swingable supports, a separate elastic strip of wire gauze secured to each of said supports,'each of said strips consisting of a flat roll of thin. highly conductive wire having a plurality of windingsand extending in the longitudinal direction of said support, said'supports having edge portions engaging with and acting upon said rolls when said rolls are pressed by saidsupportsagainst the opposite sides of a commutator, whereby said rolls yieldably engage large surfaces of the commutator, each roll being merely secured to its support at the free end thereof, while the remainder of said'roll merely restson its support in the longitudinal direction thereof, and means for securing the other ends of said supports in a fixed position relatively to each other.

2. A commutator brush unit as defined in claim 1, in which said fiat roll is secured to the free end of said leaf spring by a heat treatment such as welding orsoldering.

(References on following page) FOREIGN PATENTS France. France. Germany. Germany. Great Britain.

ORIS L. RADER, Primary Examiner.

MILTON O. HIRSHFIELD, DAVID X. SLINEY,

Examiners. 

1. A COMMUTATOR BRUSH UNIT FOR A MINIATURE MOTOR, COMPRISING A PAIR OF SWINGABLE SUPORTS, A SEPARATE ELASTIC STRIP OF WIRE GAUZE SECURED TO EACH OF SAID SUPPORTS, EACH OF SAID STRIPS CONSISTING OF A FLAT ROLL OF THIN HIGHLY CONDUCTIVE WIRE HAVING A PLURALITY OF WINDINGS AND EXTENDING IN THE LONGITUDINAL DIRECTION OF SAID SUPPORT, SAID SUPPORTS HAVING EDGE PORTIONS ENGAGING WITH AND ACTING UPON SAID ROLLS WHEN SAID ROLLS ARE PRESSED BY SAID SUPPORTS AGAINST THE OPPOSITE SIDES OF A COMMUTATOR, WHEREBY SAID ROLLS YIELDABLY ENGAGE LARGE SURFACES OF THE COMMUTATOR, EACH ROLL BEING MERELY SECURED TO ITS SUPPORT AT THE FREE END THEREOF, WHILE THE REMAINDER OF SAID ROLL MERELY RESTS ON ITS SUPPORT IN THE LONGITUDINAL DIRECTION THEREOF, AND MEANS FOR SECURING THE OTHER END OF SAID SUPPORTS IN A FIXED POSITION RELATIVELY TO EACH OTHER. 